In order for a rare, massive star to form inside an interstellar cloud of gas and dust, small "helper" stars about the size of the sun must first set the stage, according to a new theory proposed by astrophysicists at the University of California, Berkeley, and Princeton University. Massive stars between 10 and 150 times the mass of the sun are few in number but produce the bulk of the heavy elements in a galaxy when they explode in supernovas. Their extreme brightness makes them signposts of star formation in distant galaxies.
What is the magic "X factor" that determines which stars become the biggest and brightest in the universe? The answer, new calculations suggest, is how dense their parent gas clouds are. Denser clouds heat up more evenly, preventing the clouds from fragmenting into lots of tiny stars and allowing one or two big stars to form instead. The research suggests astronomers may be underestimating the number of small- to medium-sized stars in the universe.